1. Field of the Invention
The invention relates to a cathode ray tube, which displays a main picture in a single color, and a method of displaying pictures.
2. Description of the Related Art
In recent years, a number of picture display devices capable of displaying a color picture have been developed. Devices displaying a picture in monochrome (single color), such as what are called monochrome display devices, also have been in demand and have been developed. For example, in the field of front-door intercoms, color picture displays using liquid crystal display devices are of use. However, monochrome display devices using a flat type cathode ray tube (flat CRT) with relatively low costs also are often in use, since color liquid crystal display devices have relatively high costs.
A flat CRT has a configuration in which electron guns and a fluorescent screen are provided on the same plane, and electron beams are emitted obliquely on the fluorescent screen, unlike a straight-type CRT in which electron beams are emitted from the electron guns vertically to the center of the fluorescent screen. A straight-type CRT is capable of color picture display by discriminating three electron beams producing red (R), green (G) and blue (B) through a color selection mechanism and by emitting the electron beams on a fluorescent screen comprising three kinds of phosphor emitting in red, blue and green. A flat CRT for displaying a monochrome picture displays a monochrome picture by, for example, forming the whole fluorescent screen by white emitting phosphor and scanning the fluorescent screen by a single electron beam. The flat CRT is often used for, for example, the picture display unit of a master apparatus of a front-door intercom or the monitor of a portable television set, since the flat CRT can be formed thinner than the straight-type CRT.
In a flat CRT for a monochrome display, there is also the case where a color picture display is partially preferred. A front-door intercom with various kinds of sensors, such as a fire detector, and a gas detector serves as a security system as a whole. In such a system, it is desirable, in the master apparatus, to notify the user by displaying the emergency in a different color (for example, red) from the regular color used for the main picture display, so that users can be alerted. However, in a front-door intercom of the related art using a flat CRT for a monochrome display, it is necessary to provide a separate device for a color display in addition to the regular picture display using the flat CRT, in order to display a warning in case of emergency. An example of a device for color a display used in a front-door intercom of the related art is one in which the light of a lamp in a predetermined color (for example, white or red) is emitted from the reverse side onto a transparent substrate to which patterns, such as letters or figures, are color-printed so that the color-printed areas emit light.
In the display method mentioned above, the warning effect is poor since, for example, the warning is displayed simply by a red lamp or the like, so that the picture display is monotonic. In the related art, it is necessary to physically provide a display area separate from the main picture display area by providing a display device only for color display in addition to the flat CRT, which displays the main picture. This could be an obstacle to miniaturizing the device.
There are still other problems. For example, in the case where a device for color display is composed of a lamp and a color-printed substrate, the cost of providing electric wiring is required in addition to the lamp and the color-printed substrate. Furthermore, in the related art, the design of the device becomes limited since it is necessary to separately provide the display area for warning.
In the front-door intercom and the like of the related art, if a specific figured picture indicating warning and the like is to be displayed by only using a CRT without separately providing a display device for warning only, it is necessary to provide a character signal generator for providing the picture to be displayed. In such a device structure, the portion with black-level signals is formed by blanking picture signals inputted in a normal state. Then, the picture signals generated by the character signal generator are superimposed on the portion with black-level signals or the picture signals generated by the character signal generator are directly superimposed on the picture signals inputted in a normal state. Thereby, a picture indicating warning and the like is displayed. However, in such a device structure, it is necessary to provide a character signal generator for making a specific picture, which is costly. Also, if a method of picture display by such structure is applied to a flat CRT for monochrome display, all of the picture can be only displayed in monochrome. Therefore, even if the method is used for a picture display for warning, the warning effect is poor.
The invention has been designed to overcome the foregoing problems. An object of the invention is to provide a CRT and a method of picture display, which can easily perform picture display in colors different from that of the main picture display.
The CRT of the invention displays a main picture in a single color and comprises: an electron gun for emitting electron beams; a first picture display unit including a phosphor which emits a single color upon incidence of electron beams while displaying a main picture by emission of the single color emission phosphor; and a second picture display unit including another phosphor which emits a color different from the single color emission phosphor upon incidence of the electron beams in a region different from the region where the single color emission phosphor is provided for displaying another picture in a color different from that of the display of the main picture by emission of the other phosphor.
The method of displaying a picture of the invention is a method in which a CRT displays a main picture in a single color, wherein a phosphor emitting a single color upon incidence of electron beams is provided and a main picture is displayed in a single color by emission of the single color emission phosphor, and another phosphor emitting a color different from the single color emission phosphor upon incidence of electron beams is provided in a region different from the region where the single color emission phosphor is provided, and another picture is displayed in another color different from the main picture by emission of the another phosphor.
In the CRT and the method of displaying a picture of the invention, a main picture is displayed in a single color by emission of the single color emission phosphor, and another picture is displayed in another color different from the main picture by emission of another phosphor provided in a region different from the region where the single color emission phosphor is provided.
In the invention, the single color emission phosphor is, for example, a white emission phosphor that emits in white. The white emission phosphor includes, in addition to a phosphor emitting white by itself, a phosphor composed of, for example, a blue emission phosphor and a yellow emission phosphor mixed in an appropriate proportion so as to look like a white emission phosphor. Also, in the invention, a single color does not only mean a single wavelength region of light but includes the case where a plurality of wavelength regions of light are mixed and recognized as a single color by the eyes of human beings.
Other and further objects, features and advantages of the invention will appear more fully from the following description.